It's the awesome thing you didn't even know you desperately needed. Dr. Horrible himself, Neil Patrick Harris, guest stars in a special episode of Adventure Time next Monday — and now the show is Adventure Time with Fionna and Cake!

Here's what Cartoon Network told us:

Neil Patrick Harris stars as Prince Gumball in "Adventure Time with Fionna and Cake", a gender-swapping, parallel universe episode featuring the female "Fionna" and her cat "Cake."

And Prince Gumball sings an ode to Fionna, as you can see in the above clip!